Method for making overbased PVC stabilizer

ABSTRACT

An overbased mixture of aliphatic and aromatic carboxylates salts useful in making low-fogging thermal stabilizers for PVC is made by reacting zinc oxide with fatty acid and such as stearic acid, then adding aromatic acids, and then adding and reacting one or both of magnesium oxide and calcium oxide, under controlled heating conditions to maintain fluidity while minimizing side reactions, and then conditioning the reaction product to remove volatiles.

BACKGROUND OF THE INVENTION

The present invention relates to stabilizer compositions for polyvinylchloride resins and to polyvinyl chloride resin compositions havingimproved resistance to degradation caused by heat coupled with a reducedtendency to emit "fog" of volatilized components. Although capable of avariety of uses, this invention finds advantageous utility in providingimproved long term stability at moderate temperatures to motor vehiclecomponents shaped from polyvinyl chloride resin compositions, especiallywhere the polyvinyl chloride resin compositions are used in combinationwith urethane.

The problem of imparting to polyvinyl chloride a sufficient heatprocessing stability at temperatures at which the polymer becomessufficiently fluid or softened to permit shaping is of course of longstanding, and has been satisfactorily resolved by addition to thepolymer of various combinations of known heat stabilizers. At processingtemperatures, the resin can degrade, liberating hydrogen chloride, anddiscolor, become brittle, and stick to the equipment. These problems areovercome by combining with the polymer before heat processing or duringheat processing one or more of the well established and successfulconventional heat stabilizers, such as, for example, organotinstabilizers and/or barium-cadmium or barium-zinc salt stabilizers.

Although the well established and successful conventional heatstabilizers provide effective stabilization to the polymer at elevatedheat processing temperatures during standard processing, they may notprovide effective stabilization to the polymer at lower more moderatetemperatures after such heat processing. For example, protection againstdiscoloration at moderate temperatures over long periods is a particularproblem with motor vehicle components shaped from polyvinyl chlorideresin compositions despite such compositions having containedconventional heat stabilizers during their heat processing. Dependingupon their location in the vehicle, these components may be exposed tovaried amounts of light, and also different rather high (above ambient)temperatures in use, and these differences can degrade motor vehiclecomponents at differing rates. One result is the volatilization of oneor more components, or of decomposition products therefrom, whichcondense as "fog" on interior surfaces such as the windows andwindshield. Additionally, .when polyvinyl chloride resin compositionsare associated with a polyurethane foam backing, e.g. automobileinstrument panels, glove compartments, door handles, arm and head rests,the amine from the urethane can contribute to discoloration of thepolyvinyl chloride resin composition.

DISCUSSION OF THE PRIOR ART

A number of stabilizing systems have been proposed for impartingpolyvinyl chloride resin articles molded with a polyurethane foambacking with resistance to deterioration from exposure to long termmoderate heat and from exposure to an amine from urethane. For example,the art has recognized the use of perchlorate salts in polyvinylchloride resin stabilization and in particular in stabilizing polyvinylchloride that is used in contact with polyurethane foam or plastic. Thisart, however, does not address the problem of "fog" and does not suggesthow to alleviate that problem. For, instance, European PatentApplication No. 861111174.8 discloses polyvinyl chloride resinstabilizer compositions comprising a 2,2, 6, 6-tetramethyl piperidinylcompound and an ammonium or metal perchlorate. This publication alsodiscloses the use of such stabilizer compositions for polyvinyl chlorideresin articles molded with polyurethane foam backing.

U.S. Pat. No. 4,861,816 discloses polyvinyl chloride compositionscontaining a stabilizer mixture of certain barium/zinc carboxylic acidsalts and a metal perchlorate and/or perchlorate ion type hydrotalcite.According to the '816 patent the perchlorate and perchlorate ion typehydrotalcite compound give excellent amine resistance, particularly tourethane attached polyvinyl chloride sheets. U.S. Pat. No. 5,225,108also discloses the use of metal perchlorates in PVC stabilizers, butdoes not address how to remedy the formation of "fog".

Other patents disclose PVC stabilizers but do not address the problemsof "fog" formation nor or interaction with polyurethane components. Forinstance, U.S. Pat. No. 3,396,132 and U.S. Pat. No. 5,102,933 disclosemagnesium-zinc benzoate-stearate stabilizers with polyhydric alcoholsand, in the case of U.S. Pat. No. 5,102,933, with beta-diketones. U.S.Pat. No. 4,950,704 also discloses the use of betadiketones for PVCstabilizers. None of these patents addresses the problem the tendency ofthe stabilized PVC to form "fog". U.S. Pat. No. 4,123,399 disclosescombinations of beta diketones and polyhydric alcohols but it, too, doesnot suggest how to reduce the tendency of the stabilized PVC to form"fog".

There remains a need for PVC stabilizers which reduce the tendency ofthe stabilized PVC composition to form "fog" upon moderate heating, yetwhich retain heat stability and satisfactory processability in thestabilized PVC composition.

BRIEF SUMMARY OF THE INVENTION

The present invention satisfies the aforementioned objectives andaffords as well the other advantages described herein.

One aspect of the present invention is a process for producing a mixtureof carboxylate salts of one or more aromatic acids and one or morealiphatic acids containing at least about 16 carbon atoms with zinc andone or both of magnesium and calcium, comprising:

(a) dissolving zinc oxide in a molten acid precursor composed of an atleast stoichiometrically equivalent quantity of said one or morealiphatic acids wherein up to about 10 mole percent of the amount ofsaid one or more aliphatic acids present is replaced by one or more ofsaid aromatic acids, in the presence of a small amount of watereffective to increase the rate of reaction of said zinc oxide with saidone or more acids, under conditions effective to achieve completereaction between said zinc oxide and said acid precursor to maximizeformation of the corresponding zinc carboxylate while minimizingformation of other reaction products and to provide thereby a liquidreaction product;

(b) adding said one or more aromatic acids to said liquid reactionproduct under conditions effective to maintain it in the liquid statewhile minimizing side reactions between said zinc carboxylate and saidaromatic acids, wherein the mole ratio of said one or more aromaticacids to aliphatic carboxylates is 0.5:1 to 2:1;

(c) adding one or more of magnesium oxide, magnesium hydroxide, calciumoxide and calcium hydroxide to the product of step (b), in an amounteffective to provide a stoichiometric excess thereof of up to about 2wt. % based on the carboxylate, under conditions effective to achievecomplete reaction of said one or more aromatic acids with said addedcompound or compounds to form said mixture of carboxylate salts whileminimizing formation of side reaction products; and

(d) conditioning the product of step (c) under conditions effective tovolatilize and remove therefrom unreacted products and side reactionproducts.

In preferred embodiments of this invention, the aforesaid aliphatic acidis an alkanoic or alkenoic acid containing at least about 18 carbonatoms, more preferably stearate.

Polyvinyl chloride formulations which are stabilized againstheat-mediated degradation and which exhibit a reduced tendency tovolatilize upon exposure to moderate heat, comprise a polyvinyl chloridepolymer and a heat stabilizer which comprises an effective amount ofsalt mixtures made using the process of the present invention. Suchpolyvinyl chloride formulations are particularly useful in thefabrication of shaped motor vehicle components, especially componentscomprising PVC and polyurethane.

DETAILED DESCRIPTION OF INVENTION

The reduced tendency of a polyvinyl chloride composition to form "fog"in use is also expressed herein as a reduced tendency of the compositionto volatilize, by which is meant that the composition emits a reducedamount of, and preferably little or no, compounds into the ambientatmosphere when the composition is exposed to moderate heat, typicallytemperatures of about 60° to 130° C. (140° to 270° F.). Such compoundsemitted by polyvinyl chloride compositions under such conditions cancomprise one or more components of the polyvinyl chloride compositionitself, products of the degradation of one or more components of thepolyvinyl chloride composition, compounds formed by the reaction of anysuch emitted compounds or degradation products, or mixtures of any ofthe foregoing.

The present invention forms an overbased mixture that includes metalsalts of one or more aromatic acids. The metal salts can be formed oftwo, or more, of the group consisting of calcium, magnesium, zinc, andbarium. Preferably, barium is not present in the stabilizer compositionat all, because of its reputed implication in health and environmentalconcerns. Also, it is preferred that the composition contains zinc. Theterm "aromatic acids" is used herein to mean benzoic acid wherein thephenyl ring either is unsubstituted, or is substituted with one, two orthree alkyl groups each of which can contain 1 to 6 carbon atoms and canbe straight or branched. Examples of such alkyl substituents includemethyl, and tert-butyl. A preferred example of such a substitutedbenzoic acid is any toluic acid, such as meta-toluic acid. Mixtures ofsubstituted and unsubstituted benzoic acid salts can also be used.

The mixture of salts also includes one or more salts of one or morefatty alkanoic and/or alkenoic aliphatic acids. Preferably, salts ofsuch aliphatic acids are present, to impart increased lubricity. Thefatty aliphatic acids useful in this component of the present inventionhave at least about 16 carbon atoms, up to about 30 carbon atoms. Thepreferred fatty aliphatic acid is stearate. Other useful fatty acidsinclude lauric and behenic acids. The molar ratio of aromaticcarboxylate to fatty aliphatic carboxylate can effectively lie in therange of 0.5:1 to about 2:1, preferably in the range of 0.8:1 to 1.2:1.

As indicated, the mixture of salts of aromatic and fatty aliphaticacid(s) is overbased, by which is meant that the total amount of all ofcalcium, magnesium, zinc and barium present in said salt mixture exceedsthe total amount of aromatic carboxylate and fatty aliphatic carboxylatepresent, on an equivalents basis. As will be seen, in the process of thepresent invention it is the magnesium or calcium that overbases, as itis added last. The degree of overbasing, that is, the ratio of(Ca+Mg+Zn+Ba present) : (aromatic carboxylates and fatty aliphaticcarboxylates present) (on an equivalents basis) is of course greaterthan 1:1, and can range up to about 1 to 5 wt. % free oxide of theoverbasing metal. The ratio of (magnesium and calcium) to zinc presentin this mixture can typically fall in the range of 1:1 to about 2:1, ona mole basis.

The process of the present invention by which the mixture of salts ofaromatic and aliphatic carboxylatesis prepared includes the followingsteps, which will be described with reference to the preferredembodiments of the invention wherein the aliphatic acid is stearic acid,the aromatic acid component acid comprises benzoic acid and meta-toluicacids, and the magnesium and zinc salts are formed.

In the first step, the zinc aliphatic carboxylate is formed prior tointroduction of magnesium (or other base metal) and prior tointroduction of the aromatic acid component. This reaction is preferablycarried out by dissolving zinc oxide into molten stearic acid.Preferably, to control the uniformity of the reaction conditions, thezinc oxide is added gradually, in several portions. The total amount ofzinc oxide added should be equal to, or slightly less than, thestoichiometrically equivalent amount of acid present. The acid precursorcomposition to Which the zinc oxide is added is composed of the one ormore aliphatic acids, such as stearic acid, although up to about 10 molepercent of the aliphatic acid component can be replaced by one or moreof said aromatic acids. The presence of the aromatic acid is preferred,as it is believed to accelerate the reaction of the zinc oxide with thealiphatic acid. In addition, a small amount of water up to about 10% isalso preferably present in this mixture, the water having been found toincrease the rate of reaction of the zinc oxide with the aliphaticacids. However, excessive amounts of water which would disturb thefluid, monophasic consistency of the reaction mixture should be avoided.Typically, amounts of water comprising up to about 10 wt. % of thereaction mixture can be advantageously present.

The acid precursor composition to which the zinc oxide is initiallyadded should be at a temperature high enough such that the acid iscompletely molten. However, the temperature should not be so high thatthe acid or the forming carboxylate product decomposes or enters intocompeting side reactions forming side products other than the desiredzinc carboxylate. Starting temperatures of about 100° C. to 110° C. aresuitable. As the progressive portions are added, it will generally benecessary to increase gradually the temperature of this mixture, so asto maintain desired fluidity aiding the dispersion of the zinc oxideinto the product and helping to control the temperature of the productitself. However, the temperature at the point at which all the zincoxide has been added should not exceed about 160° C. Carrying out thisstep of the process of the present invention in a stirred, heatedreactor vessel is highly desirable. Preferably, each portion of zincoxide that is added to that mixture should be completely dissolvedbefore the next portion is added. Preferably, during this entire step,all water evolved from the mixture is refluxed into the mixture.

When addition of all zinc oxide is completed and the reaction thereofhas been completed, the resulting product should be maintained at atemperature sufficient to maintain fluidity of the product, whichtemperature should also be above the melting point of the aromatic acidswhich are next to be added to the mixture. Then, in the second step ofthe process of the present invention, the one or more aromatic acidssuch as meta-toluic and benzoic acids are stirred into this product. Itis preferred that this acid component is added gradually, in portions,to assist in temperature control and control of the uniformity of theproduct. The temperature of the step should be adequately controlled,typically to no higher than about 160° C. to 170° C., so as to minimizeside reactions between zinc carboxylate and the one or more aromaticacids which are added in this step. It is recognized that during thisstep there may be some equilibrium conversion of zinc aliphaticcarboxylate to zinc aromatic carboxylate, with the associated formationof the aliphatic acid. The side reactions which are preferably minimizedin this step are not that conversion but other reactions, particularlythose in which the aliphatic carboxylate and the one or more aromaticcarboxylate anions condense to form a new byproduct with associatedformation of carbonate or carbon dioxide.

It is preferred in this step that the mole ratio of the one or morearomatic acids to the aliphatic carboxylate (on an equivalence basis) is0.5:1 to 2:1, and preferably 0.9:1 to 1.1:1, such as about 1:1.

In the next step of the process of the invention, one or more ofmagnesium oxide, magnesium hydroxide, calcium oxide, and/or calciumhydroxide, preferably magnesium oxide, is added to the product of thepreceding step while that product is maintained in a heated, fluidcondition. The total amount of hydroxide(s) and oxide(s) that is addedshould correspond to a stoichiometric excess (based on the carboxylatescontent) of up to about 5 wt %. As in the previous steps, it ispreferred to add the magnesium and/or calcium oxide or hydroxidegradually, in portions, to assist in maintaining control of the reactionconditions and the physical properties such as the viscosity of theproduct. It is generally necessary to increase the temperature of theproduct gradually during the course of the addition added in this step,to maintain adequate fluidity of the product. Again, however,temperature control should be maintained so as to minimize formation ofany side reaction products other than the desired formation of thealiphatic and aromatic carboxylates of zinc and magnesium and/orcalcium. In general, this means that the temperature of the mixture willrise from typically about 160° C. at the initial addition of themagnesium and/or calcium oxide, and/or hydroxide, to 180°-200° C. at theend of the addition of magnesium and/or calcium oxide and/or hydroxide.The added compound(s) react with the acids present, to form anequilibrium mixture of carboxylates of the zinc and the one or both ofmagnesium and calcium.

In the next step of the process of the present invention, the product ofthe preceding step is conditioned to remove a substantial portion, andpreferably all, of the volatile components such as unreacted reagentsand any side reaction products that may have formed in the precedingsteps. The conditioning should be carried out at moderately elevatedtemperature, under reduced pressure, so as to remove as volatiles thosecomponents which otherwise would present a risk of volatilizing from thefinished heat stabilizer after incorporation thereof into a polyvinylchloride formulation. Typical conditioning conditions include holdingthe product at 190°-200° C., under a pressure on the order of 200 mm Hg,for about an hour. Preferably, the conditioning step can be assisted by,maintaining a nitrogen sparge though the reaction product, typically ata very low flow rate.

After this conditioning step, the product can be poured into any desiredrecepticle, cooled, hardened, and prepared for further use by means suchas crushing or grinding to an appropriate dimension facilitating itsincorporation into heat stabilizers and the like.

The overbased carboxylate products formed by the process describedherein can be used in a wide variety of heat stabilizer formulations forincorporation into polyvinyl chloride compositions, particularly thosecompositions which are intended for use in environments that couldprovoke the emission of "fog" from the polyvinyl chloride product. Thecomponents of preferred heat stabilizer compositions are describedhereinbelow.

Stabilizer compositions with which the products formed by the presentinvention are useful include those which also include a carbonate orsilicate component which is a heat stabilizer for the polyvinylchloride. Examples of such compounds abound and are well known in thefield. Preferred examples include inorganic metal silicates such asmono-or condensed silicates of sodium, calcium, magnesium, aluminum, andzinc. Other preferred examples include dimetallic and polymetalliccarbonates and silicates, such as magnesium aluminum carbonate, aparticularly preferred example of which is hydrotalcite (correspondingto the formula Mg_(1-x) Al_(x) (OH)₂ (CO₃)_(x/2) ·mH₂ O wherein x isbetween 0 and 1). Yet other preferred examples include sodium aluminumsilicates, and calcium aluminum silicates, especially zeolites.

Another component of the stabilizer compositions, which is optional butpreferred, is a polyol component comprising one or more polyol compoundscontaining 2 to 10 hydroxyl groups. The polyols useful in this inventioncontain generally 2 to 20 carbon atoms, and may contain 1 or more heteroatoms such as, especially, one or more nitrogen atoms. Examples ofsuitable polyol compounds include ethylene glycol, propylene glycol,glycerol, sorbitol, mannitol, xylitol, pentaerythritol,dipentaerythritol, tripentaerythritol, and tris (2-hydroxyethyl)isocyanurate, which latter compound is a preferred polyol in thepractice of this invention.

To achieve the desired combination of properties using stabilizers madewith the process of the present invention, the one or more polyolscomprising the aforementioned polyol component should be present in suchan amount that the polyols do not cause the stabilizer to exhibitincreased fogging. By this is meant that the polyol should notvolatilize at all, or it should not volatilize to such an extent that itnegates the effect of the overbasing in reducing the overall tendency ofthe stabilizer to cause fogging. Subject to this consideration, theratio by weight of the overbased mixture of salts to the amount of theone or more polyols present is generally in the range of about 1:1 toabout 2:1, and more preferably about 1.5:1 to about 2:1. The polyoltris(2-hydroxyethyl) isocyanurate is particularly preferred because ofits low fogging behavior.

It has been determined that the presence of the additional overbasingamount of magnesium, or calcium, beyond the amount necessary to achieveneutralization of the aromatic carboxylate and of any fatty alkanoicand/or alkenoic carboxylate present, provides a significant andunexpected improvement in that the stabilizer composition exhibits agreatly reduced tendency to cause "fogging" (that is, a reduced tendencyto volatilize when heated to moderately elevated temperatures). Inaddition, the polyol component contributes improved heat processingstability without contributing to windshield fogging, that is, withoutcontributing to volatilization of the stabilizer component. Furthermore,these stabilizer compositions contribute, to polyvinyl chloride resincompositions containing these compositions, satisfactory stabilityagainst heat-mediated degradation and satisfactory processing stability.The overbased carboxylate composition does not detract from thestability against heat-mediated degradation and processing stability ofthe polyvinyl chloride formulations containing this stabilizer.

Stabilizer compositions using products of the process of the presentinvention preferably include one or more optional but preferredconstituents. One such constituent is a beta-diketone componentcomprising one or more beta-diketones having the structural formula R¹--C(O)--CH₂ --C(O)--R² wherein R¹ is alkyl having about 10 to about 30carbon atoms, and R² is phenyl, phenyl substituted with up to 3 lower(C₁ -C₆) alkyl groups, or alkyl containing 1 to 30 carbon atoms.

Examples of suitable beta-diketones include benzoylacetone,lauroylbenzoylmethane, myristoylbenzoylemethane,palmitoylbenzoylmethane, stearoylbenzoylmethane, behenoylbenzoylmethane,dilauroylmethane, dimyristoylmethane, dipalmitoylmethane,distearoylmethane, dibehenoylmethane, lauroylmyristoylmethane,lauroylpalmitoylmethane, lauroylstearoylmethane, lauroylbehenoylmethane,myristoylpalmitoylmethane, myristoylstearoylmethane,myristoylbehenoylmethane, palmitoylstearoylmethane,palmitoylbehenoylmethane, stearoylbehenoylmethane, lauroyl toluylmethane, stearoyl toluyl methane, lauroyl xyloyl methane, stearoylxyloyl methane, 1-phenyltriacontane-1, 3-dione, acetyltetralone,palmitoyltetralone, stearoyltetralone, palmitoylcyclohexanone,stearoylcyclohexanone and (paramethoxybenzoyl)-stearoylmethane. Thesecompounds are utilized in amounts of between about 0.05 and 5% by weightrelative to the weight of the PVC and, preferably, between about 0.1 and1% by weight.

It is also advantageous to include in the stabilizer compositions or inpolyvinyl chloride products containing the stabilizer compositions, aperchlorate component comprising one or more perchlorate compounds.Examples include metal-perchlorate salts such as barium perchlorate,magnesium perchlorate, aluminum perchlorate, sodium perchlorate, calciumperchlorate, and the like. Other examples include the sodiumperchlorate/calcium silicate composition disclosed in U.S. Pat. No.5,225,108, the disclosure of which is hereby incorporated herein byreference. Other examples include perchlorate-derivatized hydrotalcitecompounds such as those disclosed in U.S. Pat. No. 4,861,816, thedisclosure of which is hereby incorporated herein by reference. Thelatter compounds are said to correspond to the formula Mg_(1-x) Al_(x)(OH)₂ ·(ClO₄)₂ ·mH₂ O wherein m represents a positive number and x isgreater than 0 and is less than or equal to 0.5.

The perchlorate helps to retard or prevent discoloration and chemicalinteraction between polyvinyl chloride and adjacent polyurethanematerials, such as encountered in shaped automobile parts. Parts can be"adjacent" yet subject to such undesired interaction if they are inphysical contact with each other or if they are near each other, nottouching, such that an amine byproduct from the polyurethane volatilizesand comes into contact with the polyvinyl chloride formulation. The oneor more perchlorate compounds are preferably present in an amount whichis about 10 to about 40 wt. % of the stabilizer composition, and morepreferably about 15 to about 35 wt. % of the stabilizer composition.

The stabilizer compositions are preferably used to advantage incombination with vinyl halide resins, preferably polyvinyl chlorideresins. The term "polyvinyl chloride" as used herein is inclusive of anypolymer formed at least in part of the recurring group (--CHCl--CX₂--)_(p) and having a chlorine content in excess of 40%. In this formula,each of the X groups can be either hydrogen or chlorine, and p is thenumber of units in each polymer chain. In polyvinyl chloridehomopolymers, each of the X groups is hydrogen. Thus, the terms, "PVC"and "polyvinyl chloride" include not only polyvinyl chloridehomopolymers but also after--chlorinated polyvinyl chlorides, as well ascopolymers of vinyl chloride in a major proportion with othercopolymerizable monomers in moderate proportion such as copolymers ofvinyl chloride and vinyl acetate, copolymers of vinyl chloride withmaleic or fumaric acids or esters, and copolymers of vinyl chloride withstyrene. The stabilizer compositions are effective also with mixtures ofpolyvinyl chloride in major proportion with a minor proportion of othersynthetic resins such as chlorinated polyethylene or copolymers ofacrylonitrile, butylene and styrene.

Stabilizer compositions incorporating a product of the process of thepresent invention can be used with plasticized polyvinyl chloride resincompositions of conventional formulation. Conventional plasticizers wellknown to those skilled in the art can be employed such as, for example,dioctyl phthalate, octyl diphenylphosphate, and epoxidized soybean oil.Particularly useful plasticizers are the epoxidized esters having form20 to 150 carbon atoms.

The stabilizer compositions are used in small amounts effective toimpart resistance to heat-mediated deterioration of the PVC or otherpolyvinyl chloride resin. That is, "heat-mediated deterioration"includes deterioration which is due to exposure to excessive heat, aswell as deterioration which is initiated or accelerated by exposure toheat. Effective heat stability is afforded generally by adding about 0.5to about 5 phr (parts by weight per hundred parts by weight of thepolyvinyl chloride) of the stabilizer. Preferred amounts are generallyin the range of about 1 to about 4 phr. The stabilizer can be compoundedinto the resin formulation in accordance with conventional compoundingtechniques abundantly familiar to one of ordinary skill in this art,wherein the stabilizer is finely divided so as to aid its dispersibilityinto the resin and is then dispersed therein by physical mixing means.

The stabilized polyvinyl chloride resin composition comprising thesecomponents can also contain conventional additional additives such asantioxidants, lubricants, flame retardants, fillers, pigments, UVabsorbers and the like, in relative amounts effective to fulfill thedesired functions of each such ingredient. These ingredients can beadded, if desired, prior to, during, or subsequent to the step in whichthe heat stabilizer composition of the present invention is compoundedinto the polyvinyl chloride composition.

Among the preferred antioxidants are phenolics, generally used inamounts up to about 0.5 wt. % of the polyvinyl chloride resincomposition, such as 2,6-di-t-butyl-4-methylphenol,2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, n-propylgallate,n-dodecylgallate, dilauryl thiodipropionate, and the like.

Each of the starting materials used herein, whether intended to bereactants or as unreacting additives, should be provided in ahigh-purity form, preferably 97% or higher purity, and free of existingvolatilized contaminants.

The invention is further described in the following example, which isincluded for purposes of illustration and not for limitation of thescope of that which the applicants consider to be the invention.

EXAMPLE 1

Under a nitrogen flow of 0.6 liters per minute, 571.5 g stearic acid (90wt. % purity) and 23.5 g benzoic acid were charged into a reactorequipped with a stirrer and an electrical heating mantle at roomtemperature. Electrical heating was started to melt the material. Thetemperature slowly increased to 100°-105° C. when the mixture of acidswas completely melted. At this point 10 ml water and 22.6 g ZnO werecarefully added under vigorous stirring and the temperature increased to120° C. When the ZnO was completely dissolved (usually after 10-15 min.)an additional 60 g ZnO was charged in six portions of 10 g, each after10 min. Each portion of Zno should be dissolved before the next portionis added. After the third portion the temperature was increased to 140°C. After the last portion, the temperature was increased to 160° C. andthe mixture stirred until all ZnO was completely dissolved (15-20 min.).During the ZnO addition total reflux of the water was maintained.

When all ZnO was dissolved and 160° C. was reached, 139 g m-toluic and100 g benzoic acids were charged in portions, while maintaining thetemperature above 140° C. To the homogeneous liquid mixture at 160° C.,10 g MgO was added. .When the reactrod with MgO had moderated, the rest(58 g) was charged in four portions of 10 g MgO and the last one of 18gMgO. The first two were charged at 30 min intervals and the rest after15 minutes. At the beginning the MgO completely dissolved but after thestoichiometric amount had been added, the rest of the MgO remained insuspension. After the second portion of MgO the temperature wasincreased to 170° C. and after the fourth portion to 180° C. After theMgO addition was completed the reaction mixture was kept at 195°-200° C.for 1.0 hour under a pressure of 200 mmHg and a very low sparge ofnitrogen. The resulting material was poured into pans, and after coolingand hardening it was chopped and ground.

The product when compounded into PVC in stabilizers gave a good thermicstability of PVC. The product itself ("neat") and in PVC compounds emitsno fog, and has a low lubrication effect on PVC.

What is claimed is:
 1. A process for producing an overbased mixture ofcarboxylate salts of one or more aromatic acids selected from the groupconsisting of benzoic acid and benzoic acid substituted with one, two orthree alkyl groups each of which contain from 1 to 6 carbon atoms, andone or more aliphatic fatty acids containing about 12 to 30 carbon atomswith zinc and of magnesium, comprising:(a) dissolving zinc oxide in amolten acid precursor composed of at least a stoichiometricallyequivalent quantity of said one or more aliphatic fatty acids wherein upto about 10 mole percent of the amount of said one or more aliphaticfatty acids present is replaced by one or more of said aromatic acids,in the presence of water in an amount up to about 10 wt %, said amountof water being effective to increase the rate of reaction of said zincoxide with said one or more aliphatic fatty acids, under conditionseffective to achieve complete reaction between said zinc oxide and saidacid precursor to maximize formation of the corresponding zinccarboxylate while minimizing formation of other reaction products and toprovide thereby a liquid reaction product; (b) adding said one or morearomatic acids to said liquid reaction product under conditionseffective to maintain it in the liquid state while minimizing sidereactions between said zinc carboxylate and said aromatic acids, whereinthe mole ratio of said one or more aromatic acids to aliphaticcarboxylates is 0.5:1 to 2:1; (c) adding magnesium oxide, eithermagnesium hydroxide, or mixtures thereof to the product of step (b), inan amount effective to provide a stoichiometric excess thereof up toabout 5 wt. % based on the carboxylate, under conditions effective toachieve complete reaction of said one or more aromatic acids with saidadded compound or compounds to form said mixture of carboxylate saltswhile minimizing formation of side reaction products; and (d)conditioning the product of step (c) under conditions effective tovolatilize and remove therefrom unreacted products and side reactionproducts.
 2. The process of claim 1 wherein magnesium oxide is added instep (c).
 3. The process of claim 1 wherein in steps (a) and (c), oxideis added in successive portions and the temperature of the material towhich the oxide is added is increased over the course of said addition.4. The process of claim 2 wherein in step (a) the temperature of saidacid precursor is increased from about 100° C. when addition of zincoxide is begun, to about 160° C. after addition of zinc oxide isdiscontinued.
 5. The process of claim 2 wherein in step (c) thetemperature of said product of step (b) is increased from about 160° C.when addition thereto is begun, to about 180° C.-190° C. after saidaddition is discontinued.
 6. The process of claim 1 wherein said one ormore aliphatic fatty acids is stearic acid.
 7. The process of claim 1wherein said one or more aromatic acids are selected from the groupconsisting of benzoic acid, all isomers of toluic acid, and mixturesthereof.
 8. The process of claim 6 wherein said one or more aromaticacids are selected from the group consisting of benzoic acid, allisomers of toluic acid, and mixtures thereof.
 9. The process of claim 8wherein magnesium oxide is added in step (c).